1. Field of the Invention
The invention relates to a device and method for preparation of vessels by cleaning and coating the interior walls of the vessels, and more specifically, the invention relates to a device and method to provide a continuous and uniform film to interior nonplanar walls of small-diameter elongated vessels.
2. Background of the Invention
Scientific instruments commonly require preparation in order to be optimally operable. For instance, a coating may need to be applied to prevent a chemical reaction between the reagents and the chamber walls. Alternatively, a coating may be deemed necessary to give a chamber required physical properties.
Reaction chambers continue to develop in sophistication, particularly as microscale processes are utilized, and advanced forms of reactants are required.
Seamless, electrically continuous films are also necessary to optimize macro-scale processes. For example, energy efficiency is a crucial parameter for operating a linear accelerator economically and an acceleration scheme operating at high efficiency is required. Inherent inefficiencies are built into certain linear accelerator paradigms, however, such as when wake fields develop during the interaction of the electron beam and the enclosing walls. The wake fields are electromagnetic fields produced by the interaction of a beam of relativistic charged particles with nearby conducting surfaces, such as walls of a vacuum chamber. These fields remain in the ‘wake’ of the leading particles and provide driving forces that act on trailing particles, potentially causing longitudinal and transverse beam instabilities. The wake acts on the trailing particles, potentially causing beam instabilities.
As light sources, such as the Advanced Photon Source (APS) in Argonne Laboratory in Argonne, Ill., increase their output, higher currents are required, which in turn calls for protection of the electron and light conduits utilized. Continuous films must be applied to the inner surfaces of these conduits so as to allow accelerator physicists the means to modify construction materials parameters, leading to increases in the performance envelope of the light source. “Continuous” films comprise surfaces that are directly exposed to the electron beam and that electrically connect to each other.
Given the importance of the physical properties of the chamber in which reactions take place, several means are well-known for creating an inner vessel of a particular inner coating. One method of achieving a specific inner coating is to instill that coating at the time the vessel is manufactured. Methods for manufacture of a vessel with an integrated inner coating are described in patents such as U.S. Pat. No. 4,091,138. However, the '138 patent and other similar methods have a number of drawbacks. First, when a material is integrally coated at the time of the manufacture, the purpose of the material must not significantly change over the course of its useful life. Inasmuch as the vessel is integrally molded or cast with the coating material, it cannot be used for another purpose that would require a different inner coating. Further, a process that instills a coating at the time of the manufacturing cannot be used at a later time when the same coating has to be reapplied.
An approach for achieving a coating on a vessel or work piece is also disclosed by U.S. Pat. No. 4,790,262. That invention uses a centrifugal force to deposit a coating by spinning the piece to be coated whilst applying a liquid coating solution to the piece. The '262 invention requires the coating material to be in a liquid state.
Sputtering is a process used to deposit a film onto a substrate whilst in a vacuum. A high voltage is passed across low pressure gas to create a plasma of electrons and ions in a high energy state. The ions hit a target of the desired coating material and cause atoms from that material to be ejected and bond with the substrate.
Several patents, such as U.S. Pat. No. 4,166,018 describe various improvements related to producing a coating of varying thickness. These devices have significant shortcomings, however. Several sputtering devices only work to coat flat surfaces. As a result, devices such as the '018 patent are hard pressed to sputter a coating on a surface that already has been turned into a closed vessel such as a round tube.
While some coated planar substrates can be curved after the coating process occurs, radii of such curvatures are limited to prevent de-lamination, weak surface adhesion, and general deformation of the coatings. As a high level of adhesion is an objective of most coating processes, and inasmuch as the rate of adhesion is directly related to energy of particles upon contact with the wall, sputtering is the preferred method as it results in particles imbued with high energy. Other coating methods, such as evaporation, do not result in high-energy particles.
Further, while the prior art discusses improvements to sputtering methods, none of the prior art references discuss a coating method which can be used with a small access aperture. Prior art coating methods based on sputtering employ strong magnetic fields and the generation of the field within the item to be coated requires a large access envelope.
Various sputtering methodologies exist. In one sputtering configuration, an ion beam is generated using a point source ion gun. Such an approach cannot be used to coat long chambers, something the present invention accomplishes through its use of a dual gas-vacuum exit scheme.
Another coating method employs Chemical Vapor Deposition (CVD). CVD-based methodologies require heating elements to be placed into the vessel to be coated. As such, they require additional space both at the insertion point and within the vessel itself. Further, CVD coating methods generate non-uniform film when used in conjunction with enclosed vessels. Also, and as noted above, such vapor deposition processes do not provide the high energy impact necessary to assure tight adhesion of coating particles and moieties to target surfaces, thereby resulting in tightly adhering, electrically continuous and blemish free films overlaying the substrates.
A need exists in the art for a device and method for facilitating the deposition of coatings on surfaces defining cavities less than 15 mm in diameter. Prior art devices are limited to applications involving tubing of a minimum diameter of 0.75 inches (19 mm) and these prior art devices cannot deposit a consistent film on a long tube. The device and method should not be limited to coating flat planes, but rather enable the coating of the entire inside of a vessel. The invention should also allow for an inner coating to be reapplied at any time, not merely at initial manufacture of the coated substrate.